Rubber composition having a crosslink distribution, its preparation and article with component

ABSTRACT

The invention relates to a rubber composition and its preparation having a crosslink distribution, particularly at least two types of crosslinks, its preparation, and an article of manufacture, including a tire, having a component of such rubber composition. In one embodiment the crosslink distribution can be a controlled crosslink distribution of at least two types of crosslinks. In one embodiment, such crosslink distribution relates to an inclusion in the rubber composition of an additive to promote the crosslink distribution where the additive itself has a part of the desired crosslink characteristics. The distributed crosslinks can be of different types including different length, different chemistry, and connecting different points on the crosslinked rubber chains. The distributed crosslinks can be present in different concentrations in the rubber composition. The crosslink distribution can be random or in the nature of a gradient change between domains of different crosslinks. The properties of the rubber composition can be varied by adjustment of such distributed crosslinks to promote various physical properties such as, for example, its viscoelastic properties, tear strength, abrasion resistance and green strength.

This application claims the benefit of currently pending U.S.application Ser. No. 13/536,266, filed on Jun. 28, 2012.

FIELD OF THE INVENTION

The invention relates to a rubber composition and its preparation havinga crosslink distribution, particularly at least two types of crosslinks,its preparation, and an article of manufacture, including a tire, havinga component of such rubber composition. In one embodiment the crosslinkdistribution can be a controlled crosslink distribution of at least twotypes of crosslinks. In one embodiment, such crosslink distributionrelates to an inclusion in the rubber composition of an additive topromote the crosslink distribution where the additive itself has a partof the desired crosslink characteristics. The distributed crosslinks canbe of different types including different length, different chemistry,and connecting different points on the crosslinked rubber chains. Thedistributed crosslinks can be present in different concentrations in therubber composition. The crosslink distribution can be random or in thenature of a gradient change between domains of different crosslinks. Theproperties of the rubber composition can be varied by adjustment of suchdistributed crosslinks to promote various physical properties such as,for example, its viscoelastic properties, tear strength, abrasionresistance and green strength.

BACKGROUND OF THE INVENTION

Polymer compositions, particularly diene-based elastomer compositions,may be cured or vulcanized, with sulfur or other means to form whatmight be referred to as a crosslinked network. Vulcanization is achemical process for converting the polymer chains of the elastomer intomore durable compositions by chemical reaction of curatives such assulfur which modify the polymer by forming crosslinks (bridges) betweenindividual polymer chains. Vehicular tires usually contain componentscomprised of sulfur cured rubber compositions.

While the mechanism of sulfur crosslinking of diene-based elastomers toform a crosslinked rubber composition may not be fully understood, boththe density of the crosslinks, or crosslink density, as well as the typeof crosslinks of the rubber composition, are understood to have aneffect on one or more of a rubber composition's physical properties. Forexample, the crosslink density of the rubber composition may be variedby changing the content of vulcanization agents such as sulfur whichthereby promotes variations in the crosslinked polymer's physicalproperties. For example, as a general rule of thumb a relatively highcrosslink density for the rubber composition promotes a more elasticmaterial. Physical properties affected by the density and the types ofcrosslinks may include but are not limited to, for example, one or moreof stiffness, fatigue, tear strength and hysteresis of the rubbercomposition. For example, see the discussion by Lake and Thomas, Proc.of the Royal Society of London, Series A, Math. and Phys. Sciences, Vol.300, No. 1460, Page 108, (1967) as well as Lawandy and Halim, Journal ofApplied Polymer Science, Vol. 96, Pages 2440 through 2445 (2005).Further, the types of crosslinks can affect physical properties of arubber composition as discussed by M. Klüppel, G. Heinrich,Macromolecules 27, Page 3596 (1994).

However, while some understanding exists relating to how the crosslinkcharacteristics affect various physical properties of a rubbercomposition, a concept of providing two or more domains of differentcrosslink characteristics in a rubber composition is to be evaluated.

This invention was first conceived by contemplating the physics ofelastomer blends. For example, a combination of two or more differenttypes of elastomers as blends of elastomers to obtain rubbercompositions with improved properties is a common procedure. In someinstances, blending two different kinds of elastomers can result inphase separation of the individual elastomers, depending somewhat upontheir miscibility (or immiscibility) with each other.

Various relationships between the chemistry of elastomer blends,morphologies of elastomer blends, individual elastomeric properties ofan elastomer blend and polymer blend/copolymer based blends ofelastomers have been evaluated.

However, for a purpose of combining different elastomers to obtain arubber composition with improved physical properties, an evaluation ofproviding varying crosslink characteristics of a rubber composition ofdifferent elastomers is to be undertaken. In particular, instead ofsimply providing a blend of different elastomers to provide rubbercompositions of varying physical properties, an evaluation is to beundertaken for providing a blend of similar or different elastomers ofvarying miscibility with a combination of different crosslinkcharacteristics, therefore a plurality of types of crosslinks. Suchevaluation can be undertaken by application of, for example, an additivethat already exhibits an ability to provide a variety of crosslinkcharacteristics for elastomers.

For this invention, an evaluation of controlled crosslink distributions(CCDs) of varied crosslink densities and/or crosslink types within anelastomer composition with the ability to be crosslinked andparticularly sulfur curable rubber compositions, particularly rubbercompositions containing diene-based elastomer(s), by use of acombination of sulfur-containing materials and free sulfur to cure, orcrosslink, the rubber composition is to be undertaken. By crosslinktype, crosslinks of different crosslink length, chemistry, andconnecting different binding points on the crosslinked polymer chainsare to be considered.

For such evaluation, it is contemplated that a distribution of crosslinkdensities and/or types within a sulfur curable elastomer-containingrubber composition could be prepared with crosslinks formed by acrosslink promoting additive CPA(1) together with crosslinks formed by asulfur curative, alternately by an organoperoxide curative, to therebypromote formation of a distributed crosslink density and type within thesulfur curable elastomer-containing rubber composition.

Also, for such evaluation, it is further contemplated that adistribution of crosslink densities and/or types within a sulfur curableelastomer-containing rubber composition could be prepared withcrosslinks formed by a crosslink promoting additive CPA(2) for combiningwith another ingredient (e.g. elastomer substituent) in the rubbercomposition to form a crosslink composite between elastomer chains,together with crosslinks formed by a sulfur curative, alternately by anorganoperoxide curative, to thereby promote formation of a distributedcrosslink density and type within the sulfur curableelastomer-containing rubber composition.

Representative of such ingredients (which may include substituents on anelastomer), for combining with said CPA(2) are, for example:

(A) functional groups contained on the elastomer such as example, amine,siloxy, hydroxyl and carboxyl groups and

(B) coupling agents having a moiety reactive with the CPA(2) and anothermoiety interactive with diene-based elastomers such as, for example,coupling agent comprised of:

-   -   (1) bis(3-trialkylsilylalkyl)polysulfide having an average of        from about 2 to about 4 connecting sulfur atoms in its        polysulfidic bridge, and    -   (2) alkoxyorganomercaptosilane.

Representative of such bis(3-trialkoxysilylalkyl)polysulfide iscomprised of, for example, bis(3-triethoxysilylpropyl)polysulfide.

For illustrative purposes to depict an idealized complex crosslinkednetwork of a plurality of differentiated crosslinks, exemplary of suchCPA(2) promoted crosslinking (crosslinked elastomer) through interactionwith (combining with) participating ingredients is illustrated by anidealized formula (A) in which the (—X-CPA(2)-X—) illustrates aformative plurality of crosslinks between elastomer chains and the (Sy)illustrates formative sulfur (polysulfur, for example) crosslinksbetween elastomer chains:

where S_(y) represents at least one and alternately (more usually) anaverage of from 2 to 8 connecting sulfur atoms, with y thereforerepresenting a value of 1 to at least 4 and alternately (more usually)an average of from 2 to and including 4, and

where X represents:

(1) at least one functional group contained on the elastomer such as,for example, amine, siloxy, hydroxyl and carboxyl groups, or

(2) coupling agents having a moiety reactive with the CPA(2) and anothermoiety interactive with diene-based elastomers such as, for example,coupling agent comprised of:

-   -   (a) bis(3-trialkylsilylalkyl)polysulfide having an average of        from about 2 to about 4 connecting sulfur atoms in its        polylsulfidic bridge, and    -   (b) alkoxyorganomercaptosilane.

For further illustrative purposes to depict an idealized complexcrosslinked network of a plurality of differentiated crosslinks,exemplary of such CPA(1) promoted crosslinking (forming a crosslinkedelastomer) through interaction with (combining with) elastomer chains isillustrated by an idealized formula (B) in which the (-CPA(1)-)illustrates a formative plurality of crosslinks between elastomer chainsand the (S_(y)) illustrates formative sulfur (polysulfur, for example)crosslinks between elastomer chains:

where S_(y) represents at least one and alternately (more usually) anaverage of from 2 to 4 connecting sulfur atoms, with y thereforerepresenting a value of 1 to at least 4 and alternately (more usually)an average of from 2 to and including 4.

It is contemplated that such CPA additive, namely said CPA(1) andCPA(2), could be added to (mixed with) the sulfur curable rubbercomposition during its preliminary, or non-productive, mixing in theabsence of free sulfur curative, to at least partially crosslink therubber composition following which in a separate and subsequent mixingstep (productive mixing step) free sulfur curative is added (mixed). Insuch manner, then, the rubber composition would contain a distributedcrosslink network comprised of a first crosslinked network created bythe CPA additive and a second crosslink network created by the freesulfur curative.

In the description of this invention, the terms “rubber”, “elastomer”and “rubbery polymer” may be used interchangeably unless otherwiseindicated. The terms “cured”, “crosslinked” and “vulcanized” may be usedinterchangeably unless otherwise indicated.

The term “phr” refers to parts by weight of a non rubber ingredient per100 parts by weight of rubber in a rubber composition.

Such terms are known to those having skill in such art.

SUMMARY AND PRACTICE OF THE INVENTION

In accordance with this invention, a method of providing a rubbercomposition with a crosslink distribution (e.g. combination of at leasttwo types of crosslinks) is comprised of:

(A) blending a rubber composition in at least one sequential preliminarymixing step (preferably in an internal rubber mixer) in the absence offree sulfur rubber curative (to a temperature in a range of for exampleabout 130° C. to about 180° C.) which is comprised of:

-   -   (1) at least one diene-based (e.g. sulfur curable, or        crosslinkable) elastomer,    -   (2) rubber reinforcing fillers comprised of:        -   (a) amorphous synthetic silica (e.g. precipitated silica),        -   (b) rubber reinforcing carbon black, or        -   (c) combination of amorphous synthetic silica (e.g.            precipitated silica) and rubber reinforcing carbon black,    -   wherein said fillers may optionally additionally contain alumina        (Al₂O₃);    -   (3) optionally a silica coupling agent for said silica (when        said silica is used) having a moiety reactive with hydroxyl        groups (e.g. silanol groups) on said silica and another,        different, moiety interactive with said diene-based        elastomer(s),

(B) subsequently mixing said rubber composition in a final and separateproductive mixing step (preferably in an internal rubber mixer) with acurative comprised of:

-   -   (1) sulfur (e.g. free sulfur or sulfur donor, preferably free        sulfur, and usually at least one sulfur vulcanization        accelerator, at an elevated temperature of, for example in a        range of from about 80° C. to about 120° C.), or    -   (2) organoperoxide, or    -   (3) combination of said sulfur and organoperoxide; followed by:

(C) molding, and curing said rubber composition (e.g. to an elevatedtemperature in a range of, for example, about 120° C. to about 200° C.);

wherein a crosslink promotion additive (CPA) comprised of at least oneof CPA(1) and (CPA(2) is added:

-   -   (1) in at least one of said preliminary mixing steps, or,    -   (2) in said final productive mixing step, or    -   (3) in a combination of at least one of said preliminary mixing        steps and said final productive mixing step.

In further accordance with this invention, a rubber composition isprovided by said method.

In additional accordance with this invention, an article of manufacture,for example a tire, is provided having a component comprised of a rubbercomposition prepared by said method.

In further accordance with this invention a rubber compositioncontaining a combination of at least two types of crosslinks is providedcomprised of:

(A) at least one diene-based (e.g. sulfur curable) elastomer, and rubberreinforcing fillers comprised of:

-   -   (1) precipitated silica,    -   (2) rubber reinforcing carbon black, or    -   (3) combination of precipitated silica and rubber reinforcing        carbon black,

(B) a crosslink network of distributed crosslinks between chains of saidelastomer(s) comprised a combination of:

-   -   (1) crosslinks derived from a CPA additive, and    -   (2) crosslinks of at curative comprised of least one of sulfur        and organoperoxide,

wherein said CPA additive is comprised of at least one of CPA(1) andCPA(2),

In further accordance with this invention, an article of manufacture isprovided having a component comprised of such rubber composition.

In additional accordance with this invention, said articles ofmanufacture is comprised of, for example, tires and engineered productscomprised of, for example, transmission belts, conveyor belts and hoses.

In further accordance with this invention, said tire component iscomprised of a tire tread.

In additional accordance with this invention, for said CPA crosslinkpromotion additive:

(A) CPA(1) is represented by a formula (I):C(BF)_(a)  (I)

(B) CPA(2) is represented by a formula (II):C(BG)_(b)  (II)

wherein

-   -   (1) C is the Core of the CPA additive,    -   (2) F is a functional group reactive with said diene-based        elastomer(s),    -   (3) G is a functional group reactive with an ingredient in the        rubber composition capable of reacting with said diene-based        elastomer(s),    -   (4) B is an optional bridge element between C and F or between C        and G;    -   (5) (a) represents the number of said optional bridge elements        in CPA(1) having a value of at least 1, alternately a value of        up to about 40, alternately in a range of from about 2 to about        40, and further alternately in a range of from about 2 to about        4, when said bridge element is present, and    -   (6) (b) represents the number of said optional bridge elements        in CPA(2) having a value of at least 1, alternately a value of        up to about 40, alternately in a range of from about 2 to about        40, and further alternately in a range of from about 2 to about        4, when said bridge element is present.

In one embodiment, for CPA (1) and CPA(2):

(A) C is selected from aliphatic hydrocarbon groups containing from 1 toabout 100, alternately from 1 to about 10, carbon atoms, from aromatichydrocarbon groups containing from about 5 to about 20, alternately fromabout 5 to about 10, carbon atoms; and from POSS cage groups comprisedof oligomeric silesquioxanes;

(B) optional B is selected from at least one of aliphatic hydrocarbongroups containing from about 1 to about 20, alternately from about 1 toabout 10, carbon atoms representative of which may be, for example,methylene, ethylene or propylene groups, aromatic hydrocarbonscontaining from 5 to about 10 carbon atoms representative of which maybe, for example, phenyl or benzyl groups, epoxy groups and acrylicgroups (e.g. methacrylic groups;

(C) F for said CPA(1) is comprised of at least one of amino groups,halogen groups, polysulfide groups containing an average of one to foursulfur atoms, epoxy groups, mercapto groups, acrylate groups (e.g.methacrylate groups), vinyl groups, thiocyanato groups, glycidoxyalkylgroups, and alkylacryloxy groups (e.g. methacryloxy groups), and

(D) G for said CPA(2) is comprised of at least one of hydroxyl groups,amino groups (e.g. primary and secondary amine groups, halogen groups(e.g. chlorine groups), epoxy groups, acrylate groups (e.g. methacrylategroups), vinyl groups, and vinyl benzyl-amino groups.

As indicated, and in an alternate embodiment, at least a portion (orall) of said CPA crosslink promoting additive, namely CPA(1) or CPA(2),may be added to the rubber composition in said final productive mixingstep together with said sulfur and/or organoperoxide curative.

It is readily envisioned that, if desired and appropriate, more than onetype of bridge element (B) may be present in the CPA (e.g. B1, B2 andB3, etc), that more than one type of functional element (F) may bepresent in the CPA(1) (e.g. F1, F2 and F3, etc), and than more than onetype of functional element (G) may be present in the CPA(2) (e.g. G1, G2and G3, etc.).

In practice, representative of said diene-based elastomer(s) are, forexample, are polymers of at least one of isoprene and butadiene andcopolymers of styrene with at least one of isoprene and 1,3-butadiene.

Representative examples of CPA(1) are, for example, and non limiting:

(A) polyhedral oligomeric silesquioxanes (POSS's) comprised of, forexample octa-[(3-mercaptopropyl) silsesquioxane represented by theformula (3-HS—C₃H₆)₈(Si₈O₁₂), (where, for illustrative purposes, the “C”component of the CPA(1) is represented by the “Si₈O₁₂” moiety, the “B”component is represented by the “C₃H₆ moiety and the “F” component isrepresented by the “SH” moiety), mercaptopropylisobutyl silsesquioxanerepresented by the formula C₃₁H₇₀0₁₂SSi₈, glycidyl POSS represented bythe formula (C₆H₁₁O₂)_(n)(SiO_(1.5))_(n) where n is 8, 10 or 12, andoctavinyl POSS represented by the formula C₁₆H₂₄O₁₂Si₈.

(B) organomercapto compounds comprised of, for example, pentaerythritoltetrakis(3-mercaptopropionate), trimethylolpropanetris(3-mercaptopropionate), 1,3-propanedithiol and 1,9-nonanedithiol,(where, for illustrative purposes, the “C” component of the CPA(1) isrepresented by the “nonane” moiety, a “B” component is non-existent) andthe “F” component is represented by “thiol” moiety, and

(C) self condensation product of abis(3-trialkoxysilylalkyl)polysulfide, said polysulfide having anaverage from 2 to about 4 connecting sulfur atoms in its polysulfidicbridge (prior to said self condensation), (e.g. self condensationproduct of a bis(3-triethoxysilylpropyl)polysulfide), (where the “C”component of the CPA(1), namely the condensation product, is representedby a resultant “—Si-(0)₃-Si—” moiety, the “B” component is representedby the “alkyl” moiety and the “F” component is represented by theresultant “broken apart sulfur” moieties created by high shear mixing ofthe polysulfide with the rubber composition at an elevated temperature).

Representative examples of CPA(2) are, for example, and non limiting:

(A) polyhedral oligomeric silesquioxanes (POSS's) comprised of, forexample at least one of octa acrylo silsesquioxane(C₆H₉O₂)_(n)(SiO_(1.5))_(n), where n=8, 10 or 12, octa glycidylsilsesquioxane (C₆H₁₁O₂)_(n)(SiO_(1.5))_(n), where n=8, 10 or 12, octavinyl silsesquioxane C₁₆H₂₄O₁₂Si₈, or octa hydroxyl silsesquioxaneSi₈O₂₀H₈, and,

(B). compounds comprised of, for example, butane-1,4-diol, (where, forillustrative purposes, the “C” component of the CPA(2) is represented bythe “butane” moiety, the “B” component is non-existent, and the “F”component is represented by the “diol” moiety), hexane-1,4-diol,1,2,4-butanetriol, or 1,2,4-benzenetriol.

Various organoperoxide curatives may be used, as may be appropriate.Representative of various organoperoxides for such purpose include, forexample, and not intended to be limiting, dicumyl peroxide;di-t-butylperoxide; benzyl peroxide; 2,5-bis(t-butylperoxy)-2,5-dimethyl hexane; 1,1-di-t-butyl peroxi-3,3,5-trimethylcyclohexane; 2,5-dimethyl-2,5-dimetyl-2,5-di(t-butyl peroxy)hexyne-3;p-chlorobenzyl peroxide; 4,4-di-(tert-butylperoxy) valerate,2,4-dichlorobenzyl peroxide; 2,2-bis(t-butyl peroxi)-butane;2,5-bis(t-butyl peroxy)-2,5-dimethyl hexane; and2,5-dimethyl-2,5-di(t-butyl peroxy)hexane.

In practice, usually, a desirable organoperoxide curative is comprisedof the dicumyl peroxide, although an alternate organoperoxide might beused alternative to, or instead of, the dicumyl peroxide, ifappropriate, having a different curative activity (e.g. different freeradical generation activity at a different temperature) is desired suchas, for example, 4,4-di-(tert-butylperoxy) valerate.

Representative of said polyhedral oligomeric silsesquioxanes (POSS) isfor example, said octa-[(3-mercaptopropyl) silsesquioxane.

Reference to polyhedral oligomeric silesquioxanes (POSS) materials, ingeneral, may be found, for example, in said U.S. Pat. No. 6,852,794 anda POSS catalog, or brochure, by Hybrid Plastics.

In one embodiment, said aforesaid silica coupling agent may be comprisedof, example, at least one of bis(3-alkoxysilylalkyl)polysulfide havingan average of from about 2 to about 4 connecting sulfur atoms in itspolysulfidic bridge and an organoalkoxymercapto silane.

In one embodiment, said bis(3-trialkoxysilylalkyl)polysulfide may becomprised of bis(3-triethoxysilylpropyl)polysulfide containing anaverage of from about 2 to about 2.6 or from about 3.2 to about 3.8,connecting sulfur atoms in its polysulfidic bridge.

Representative of said organoalkoxymercaptosilanes are, for example,triethoxy mercaptopropyl silane, trimethoxy mercaptopropyl silane,methyl dimethoxy mercaptopropyl silane, methyl diethoxy mercaptopropylsilane, dimethyl methoxy mercaptopropyl silane, triethoxy mercaptoethylsilane and tripropoxy mercaptopropyl silane.

A significant aspect of the invention is the introduction in the rubbercomposition, and therefore an inclusion in the rubber composition, of anetwork of distributed crosslink density and/or types of crosslinksformed by at least one of said CPA(1) or CPA(2) together with saidsulfur. Such distributed crosslink network in the rubber composition isprovided to promote various physical properties of the rubbercomposition intended to be beneficial to vehicular tire performance.

In practice, the rubber of said rubber composition is comprised of atleast one elastomer selected from copolymers of at least one of isopreneand 1,3-butadiene and terpolymers of styrene with at least one ofisoprene and 1,3-butadiene.

Representative examples of such elastomers are, for example, cis1,4-polyisoprene rubber (IR), (natural and synthetic), cis1,4-polybutadiene rubber (BR), styrene-butadiene rubber (SBR),styrene-isoprene-butadiene terpolymer rubber (SIBR), styrene-isoprenerubber (SIR) and isoprene-butadiene rubber (IBR) and high vinylpolybutadiene rubber (HVPBD) having a vinyl 1,2-content in a range offrom about 30 to about 80 percent.

In one embodiment, elastomers for this invention may be tin and/orsilicon coupled, preferably tin coupled, as diene-based elastomersprepared by organic solvent polymerization in the presence of a suitabletin-based catalyst complex using at least one of isoprene and1,3-butadiene monomers or of styrene together with at least one ofisoprene and 1,3-butadiene monomers. Said tin and/or silicon coupledelastomers may be selected from, for example, styrene/butadienecopolymers, isoprene/butadiene copolymers, styrene/isoprene copolymersand styrene/isoprene/butadiene terpolymers. The preparation of tin andsilicon coupled elastomers via organic solvent polymerization is wellknown to those having skill in such art.

In one aspect, the elastomers may include one or more in-chain or endfunctionalized diene-based elastomers. For example, such functionalizedelastomer may be provided as a diene-based elastomer as described abovewhich contains one or more functional groups comprised of at least oneof hydroxyl groups, carboxyl groups, amine groups, siloxy groups, thiolgroups and epoxy groups, particularly such groups which are available toparticipate in reactions with, for example, precipitated silicareinforcement.

Exemplary of functionalized elastomers, where appropriate, are such asfor example, functionalized styrene/butadiene copolymer elastomers(functionalized SBR elastomers) containing amine and/or siloxy (e.g.alkoxyl silane as SiOR) functional groups.

Representative of such amine functionalized SBR elastomers is, forexample, SLR4601™ from Styron and T5560™ from JSR, and in-chain aminefunctionalized SBR elastomers mentioned, for example, U.S. Pat. No.6,936,669.

Representative of such siloxy functionalized SBR elastomers is, forexample, SLR4610™ from Styron.

Representative of such combination of amine and siloxy functionalizedSBR elastomers is, for example, HPR350™ from JSR.

Other and additional elastomers are functionalized styrene/butadienecopolymer elastomers (functionalized SBR elastomers) containing hydroxyor epoxy functional groups.

Representative of such hydroxy functionalized SBR elastomers is, forexample, Tufdene 3330™ from Asahi.

Representative of such epoxy functionalized SBR elastomers is, forexample, Tufdene E50™ from Asahi.

In practice, it is therefore envisioned that said sulfur vulcanizableelastomer (diene-based elastomer) may be comprised of, for example,polymers of at least one of isoprene and 1,3-butadiene; copolymers ofstyrene and at least one of isoprene and 1,3-butadiene; high vinylstyrene/butadiene elastomers having a vinyl 1,2-content based upon itspolybutadiene in a range of from about 30 to 90 percent andfunctionalized copolymers comprised of styrene and 1,3-butadiene(“functionalized SBR”) selected from amine functionalized SBR, siloxyfunctionalized SBR, combination of amine and siloxy functionalized SBR,epoxy functionalized SBR and hydroxy functionalized SBR.

It should readily be understood by one having skill in the art that saidrubber composition can be compounded by methods generally known in therubber compounding art, such as mixing the various sulfur-vulcanizableconstituent diene-based elastomers with various commonly-used additivematerials such as, for example, curing aids, such as sulfur, activators,retarders and accelerators, processing additives, such as oils, resinsincluding tackifying resins, plasticizers, fillers, pigments, zincoxide, waxes, antioxidants and antiozonants, peptizing agents and theaforesaid reinforcing fillers as rubber reinforcing carbon black andsynthetic amorphous precipitated silica aggregates. As known to thoseskilled in the art, depending on the intended use of thesulfur-vulcanizable and sulfur-vulcanized materials (rubbers), thevarious additives mentioned above are selected and commonly used inconventional amounts unless otherwise indicated herein.

The pneumatic tires are conventionally comprised of a generallytoroidal-shaped carcass with an outer circumferential tread, adapted tobe ground contacting, spaced beads and sidewalls extending radially fromand connecting said tread to said beads.

Typical amounts of antioxidants may comprise, for example, 1 to about 5phr. Representative antioxidants may be, for example,diphenyl-p-phenylenediamine and others, such as those disclosed in TheVanderbilt Rubber Handbook (1978), Pages 344 through 346. Suitableantiozonant(s) and waxes, particularly microcrystalline waxes, whereused, may, for example, be of the type shown in The Vanderbilt RubberHandbook (1978), Pages 346 and 347. Typical amounts of antiozonantswhere used, may, for example, comprise 1 to about 5 phr. Typical amountsof zinc oxide may, for example, comprise from 2 to about 5 phr. Typicalamounts of waxes, where used, may comprise, for example, from 1 to about5 phr. Typical amounts of peptizers, where used, may, for example,comprise from 0.1 to about 1 phr. The presence and relative amounts ofthe above additives are not normally considered herein as a significantaspect of the present invention.

The vulcanization of the elastomer composition is conducted in thepresence of the crosslinking agents. Examples of suitablesulfur-vulcanizing agents include elemental sulfur (free sulfur) orsulfur-donating vulcanizing agents, for example, an amine disulfide,polymeric polysulfide or sulfur olefin adducts. Preferably, thesulfur-vulcanizing agent is elemental sulfur. Such sulfur-vulcanizingagents may normally used are used, for example, in an amount rangingfrom about 0.5 to about 5 phr with a range of from 1.5 to 2.3 beingoften preferred.

Accelerators are used to control the time and/or temperature requiredfor vulcanization by the sulfur vulcanization agents and to improve theproperties of the vulcanizate. In one embodiment, a single acceleratorsystem may be used, i.e., primary accelerator. Conventionally, a primaryaccelerator is used in amounts ranging from, for example, about 0.5 toabout 3 phr. In another embodiment, combinations of two or moreaccelerators might be used, if desired and where appropriate, in which aprimary accelerator is might be used in the larger amount of, forexample, from 0.5 to 1.0 phr, and a secondary accelerator which might beused in smaller amounts, for example, from 0.05 to 50 phr, in order toactivate the sulfur vulcanization process. Combinations of suchaccelerators have historically been sometimes known to produce asynergistic effect of the final properties of sulfur-cured rubbers andare sometimes somewhat better than those produced by use of eitheraccelerator alone. In addition, delayed action accelerators may be used,where appropriate which are less affected by normal processingtemperatures but might produce satisfactory cures at ordinaryvulcanization temperatures. Representative examples of acceleratorsinclude, for example, various amines, disulfides, diphenyl guanidine,thioureas, thiazoles, thiurams, sulfenamides, dithiocarbamates andxanthates, particularly diphenyl guanidine. The primary acceleratormight be, for example, a sulfenamide such as, for example,N-cyclohexyl-2-sulfenamide. If a second accelerator is used, thesecondary accelerator might be selected from, for example, the diphenylguanidine, a dithiocarbamate or a thiuram compound.

The tire can be built, shaped, molded and cured by various methods whichwill be readily apparent to those having skill in the art.

For example, such unvulcanized rubber composition can be, for example, atread rubber composition (e.g. in a form of an extruded uncured rubberstrip) which can be applied in the building of the green (unvulcanized)rubber tire in which the uncured, shaped tread is built onto the carcassfollowing which the green tire is shaped and cured.

Alternately, for a tire retreading operation, an unvulcanized, orpartially vulcanized, tread rubber strip can be applied to a cured tirecarcass from which the previous tread has been buffed or abraded awayand the tread cured thereon as a retread.

The practice of this invention is further illustrated by reference tothe following examples which are intended to be representative ratherthan restrictive of the scope of the invention. Unless otherwiseindicated, all parts and percentages are by weight.

EXAMPLE I

Rubber composition was prepared to evaluate the usage of a CPA, namelyCPA(1), to promote a controlled distribution of crosslinks in acrosslinked elastomer composition.

For this evaluation, a basic rubber composition is provided as reportedin Table 1. The parts and percentages are by weight unless otherwiseindicated.

TABLE 1 Parts (phr) First Non-Productive Mixing Step (NP) - Mixed ininternal rubber mixer to about 160° C. Styrene/butadiene rubber (SBR)¹70 Cis 1,4-polybutadiene rubber² 30 Composite of carbon black and Silicacoupling agent³ 10.4 Silica, rubber reinforcing⁴ 65 Crosslink promotingadditive, CPA(1)⁵ 0 and 0.9 Processing Oils & Wax 22 Antioxidants⁶ 2.8Zinc oxide 3.5 Productive Mixing Step (PR) - Subsequently mixed ininternal rubber mixer to about 110° C. Sulfur 1.7 Sulfur vulcanizationaccelerator(s)⁸ 3.9 ¹Functionalized Styrene/butadiene rubber (SBR),comprised of styrene/butadiene copolymer containing about 21 percentbound styrene as Sprintal ™ SLR 4602 from Styron ²High cis1,4-polybutadiene rubber as BUD1207 ™ from The Goodyear Tire & RubberCompany ³Composite of carbon black and silica coupler in a 50/50 weightratio where said silica coupler is comprised of abis(3-triethoxysilylpropyl) polysulfide having an average in a range offrom about 3.4 to about 3.8 connecting sulfur atoms in its polysulfidicbridge as Si69 ™ from Evonic ⁴Zeosil Z1165 MP ™ precipitated silica fromRhodia ⁵Thiol functionalized octa-propylsilsesquioxane(3-HS-C₃H₆)₈(Si₈O₁₂) from The Goodyear Tire & Rubber Company⁶Phenylenediamine(s) ⁸Sulfenamide and diphenyl guanidine sulfurvulcanization accelerators

Conjugated diene-based elastomer compositions were prepared based on theformulation of Table 1 and identified as rubber Samples A and B. RubberSample A is a Control rubber composition without crosslink promotingadditive CPA(1) and rubber Sample B contained the crosslink promotingadditive CPA(1).

Various physical properties are presented in Table 2 and reported inparts and percentages by weight (e.g. parts by weight per 100 parts byweight rubber, or phr) unless otherwise indicated.

TABLE 2 Rubber Composiitions A B Crosslink promoting additive, CPA(1),phr 0 0.9 Physical Properties Tensile strength at break (MPa) 12.8 13.8Elongation at break (%) 420 390 Modulus, 300%, ring, (MPa) 8.8 10.9Rebound (Zwick)  23° C. 42.8 47.6 100° C. 57.7 62.7 Abrasion rate(mg/km), Grosch¹ High severity (70N), 12° slip angle, disk speed = 133114 20 km/hr, distance = 250 meters ¹The Grosch abrasion rate run on anLAT-100 Abrader and is measured in terms of mg/km of rubber abradedaway. The test rubber sample is placed at a slip angle under constantload (Newtons) as it traverses a given distance on a rotating abrasivedisk (disk from HB Schleifmittel GmbH). In practice, a high abrasionseverity test may be run, for example, at a load of 70 Newtons, 12° slipangle, disk speed of 20 km/hr and distance of 250 meters.

It can be seen from Table 2 that, for Experimental rubber Sample B withaddition of the CPA in the non-productive mixing stage (prior to theproductive, sulfur addition, productive mixing state) resulted in anincrease of the Rebound physical property of the rubber composition at23° C. and 100° C. by at least 10 percent which is indicative ofimprovement in hysteresis of the rubber composition, an indicatedreduction in internal heat generation during the working of the rubbercomposition and a predictive reduction of the rolling resistance of atire with a tread of such rubber composition, as compared to the Controlrubber Sample A.

It can also be seen from Table 2 that the Grosch rate of abrasion valuefor the rubber composition of Experimental rubber Sample B (with theaddition of the CPA) decreased by more than 10% as compared to Controlrubber Sample A which indicates an improvement in resistance to abrasionand an indicated reduction in treadwear for a tread of such rubbercomposition.

This is considered to be significant in a sense of improving twophysical properties of the rubber composition and a predictiveimprovement in two performance properties for a tire with tread of suchrubber composition.

Therefore, it is concluded that it has been discovered that suchcontrolled distribution of crosslinks can be beneficial for thepreparation of a distributed crosslinked sulfur curable rubbercomposition with significant prospective utility for tire component, forexample, and not intended to be limited, to a tire tread.

While certain representative embodiments and details have been shown forthe purpose of illustrating the subject invention, it will be apparentto those skilled in this art that various changes and modifications canbe made therein without departing from the scope of the subjectinvention. It is, therefore, to be understood that changes can be madein the particular embodiments described which will be within the fullintended scope of the invention as defined by the following appendedclaims.

What is claimed is:
 1. A rubber composition containing a combination ofat least two types of crosslinks comprised of: (A) elastomer(s)comprised of at least one of cis 1,4-polyisoprene, cis 1,4-polybutadieneand styrene/butadiene rubber, (B) rubber reinforcing fillers comprisedof: (1) rubber reinforcing carbon black, or (2) a combination ofprecipitated silica and rubber reinforcing carbon black, together with asilica coupling agent for said precipitated silica having a moietyreactive with hydroxyl groups on said precipitated silica and another,different, moiety interactive with said diene-based elastomer(s)comprised of a bis(3-triethoxysilylpropyl) polysulfide containing anaverage of from about 2 to about 2.6 or from about 3.2 to about 3.8connecting sulfur atoms in its polysulfidic bridge, or analkoxyorganomercaptosilane, (C) a crosslink network of distributedcrosslinks between chains of said elastomer(s) comprised a combinationof: (1) octa-(3-mercaptopropyl) silsesquioxane represented by theformula (3-HS—C₃H₆)₈(Si₈O₁₂) based crosslinks, and (2) sulfur basedcrosslinks.
 2. A tire having a component comprised of the rubbercomposition of claim
 1. 3. The rubber composition of claim 1 whereinsaid reinforcing filler is comprised of said combination of precipitatedsilica and rubber reinforcing carbon black together with said silicacoupling agent for said precipitated silica comprised ofbis(3-triethoxysilylpropyl) polysulfide containing an average of fromabout 2 to about 2.6 or from about 3.2 to about 3.8 connecting sulfuratoms in its polysulfidic bridge.
 4. The rubber composition of claim 1wherein said silica coupling agent is comprised of saidbis(3-triethoxysilylpropyl) polysulfide containing an average of fromabout 2 to about 2.6 connecting sulfur atoms in its polysulfidic bridge.5. The rubber composition of claim 1 wherein said silica coupling agentis comprised of said bis(3-triethoxysilylpropyl) polysulfide containingan average of from about 3.2 to about 3.8 connecting sulfur atoms in itspolysulfidic bridge.
 6. A tire having a component comprised of therubber composition of claim
 3. 7. A tire having a component comprised ofthe rubber composition of claim
 4. 8. A tire having a componentcomprised of the rubber composition of claim 5.